Polyimide gas separation membranes

ABSTRACT

Semi-flexible aromatic polyimides, prepared by polycondensation of dianhydrides with phenylene diamines having alkyl substituents on all ortho positions to the amine functions incorporating at least in part 3,3&#39;,4,4&#39;-benzophenone tetracarboxylic dianhydride, are auto photochemically crosslinkable. Membranes formed from this class of crosslinked polyimides have improved environmental stability and superior gas selectivity than the corresponding uncrosslinked polyimide. The range of gas permeation properties observed allows for the tailoring of membrane material for widely diverse gas separations. The high permeabilities of some gases from multicomponent mixtures is due to the optimization of the molecular free volume in the polymer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to certain substituted crosslinkedaromatic polyimide gas separation membranes particularly useful forseparating gases and the process of using them.

2. Prior Art

U.S. Pat. No. 3,822,202 and U.S. Pat. No. 3,899,309 disclose aromaticpolyimide gas separation membranes in which the molecular structure issuch that the molecules in the polymer are unable to pack densely, and,therefore, have high gas permeation rates.

U.S. Pat. No. 4,113,628 and U.K. No. 1,435,151 disclose aromaticpolyimide gas separation membranes prepared from polyamide acidmembranes.

EPO No. 132,221 and EPO No. 141,781 disclose substituted aromaticpolyimides and photochemically crosslinked compositions thereof, but notfor use as gas separation membranes.

U.S. Pat. Nos. 4,370,290, 4,460,526, 4,474,662, 4,512,893, U.K. Nos.2,098,994, 2,101,137, and 2,102,333 disclose microporous aromaticpolyimide membranes and the process from which they are prepared.

U.S. Pat. No. 4,486,376 and U.K. No. 2,104,832 disclose gas separationmembranes made from a microporous aromatic polyimide support treatedwith modifying agents.

U.S. Pat. Nos. 4,378,324, 4,440,643, 4,474,858, 4,485,056, 4,528,004,U.K. Nos. 2,102,726, 2,104,411, and 2,104,905 disclose gas separationmembranes made from a microporous aromatic polyimide support coated withan aromatic polyamide acid or aromatic polyimide.

U.S. Pat. No. 4,378,400 and EPO No. 43,265 disclose aromatic polyimidegas separation membranes in which the molecular structure is such thatthe molecules in the polymer can pack densely.

U.S. Pat. No. 4,578,166 discloses polymers comprising as the essentialcomponent a saturated linear polyester or polyamide and copolymerizedtherewith benzophenone tetracarboxylic groups which are crosslinked byirradiation.

EPO No. 113,574 discloses gas separation membranes made from aromaticpolyetherimides.

EPO No. 143,552 discloses gas separation membranes made from amicroporous aromatic polyimide support coated with a crosslinkedsilicone resin film.

EPO No. 125,908 discloses aromatic polyimide reverse osmosis membranes.

SUMMARY OF THE INVENTION

The present invention relates to photochemically crosslinked aromaticpolyimide gas separation membranes in which the monomeric diamines wereat least in part selected from those substituted on essentially all ofthe positions ortho to the amino substitutents and the monomeric acidanhydride groups were at least in part 3,3',4,4'-benzophenonetetracarboxylic dianhydride. The carbonyl bridge of the dianhydrideserves as a crosslinking site. The membranes exhibit very highpermeation to gases while still being able to effectively separateseveral combinations of gases.

DETAILED DESCRIPTION

The present invention relates to the discovery that aromatic polyimidesprepared by polycondensation of dianhydrides, at least in part3,3',4,4'-benzophonetetracarboxylic dianhydrides, with aromatic diaminesat least in part having normal or iso alkyl-substituents (joined tothose ortho positions by a carbon having at least one -hydrogen atom) onall positions ortho to the amine functions and which are photochemicallycrosslinked form membranes with exceptional gas permeability and gasselectivity. The gas productivity through these crosslinked polyimidemembranes can be controlled by the amount of polyimide chain rigidityand crosslink density incorporated therein. The high gas productivitythrough these membranes is believed to be due to optimization of themolecular free volume in the polymer structure resulting from acombination of the polymer chain rigidity and crosslink density.

Generally, extremely high gas permeation through dense polymericmembranes is found only with low glass transition temperature (Tg)materials, such as silicone rubbers and a few polyolefin polymers. Thelow Tg materials are generally only useful as the dense separating layerin composite membranes, where a supporting porous membrane substructureprovides structural integrity.

High Tg polymeric materials, found in the prior art, which may possesshigh gas selectivities, do not possess extremely high gaspermeabilities. Examples reported involve mostly unsubstituted, orpartially substituted, polymers subject to forming a close chain packingduring fabrication and/or subsequent operation.

The present invention circumvents the above shortcomings and providesexceptionally high gas productivity dense membranes using crosslinkedaromatic polyimides containing the repeating unit: ##STR1## or mixturesthereof

--X,--X₁, --X₂, and --X₃ are independently primary or secondary alkylgroups having 1 to 6 carbon atoms preferably methyl or ethyl,

--Z is --H, --X, --X₁, --X₂, or --X₃ and --R" is ##STR2## (where n=0 to4) or alkylene radicals of 1 to 3 carbon atoms and from 5 to 100% R. Themultiple substitutions ortho to the amines in the above illustratedstructures sterically restricts free rotation around the imide linkage.These amines in combination with structurally rigid dianhydrides formrigid polyimides. The incorporation of more flexible units such as##STR3## for dianhydrides, allows for the partial relaxation of thisrigidity which may lead to lowered molecular free volume in the polymer.This relaxation promotes greater selectivity for the permeation ofcertain gases from multicomponent gas mixtures through the membrane. Byvarying the amount of relaxation in the polymers of this invention,membranes can be tailored for a wide range of gas separations withexceptional gas productivity.

The semi-flexible polyimides described herein are additionallyautophotochemically crosslinkable. This further restricts the molecularfree volume in the polymer allowing for greater selectivity in thepermeation of certain gases from multicomponent gas mixtures through themembrane. Optimization of the amount of relaxation in the polymers andthe crosslink density in the membrane should promote the tailoring ofmembranes for even a wider range of gas separations with improvedpermeation properties and environmental stability.

The photochemical crosslinking reaction occurs without the addition ofadded components, such as sensitizers, chain carriers and the like. Thisavoids possible complications in the membrane formation step, thephotochemical crosslinking step, or the use of the resulting membranesin gas separations. For example, if such added components were lostafter the photochemical crosslinking step through membrane extraction orother procedures, the resulting membrane may have greatly differentgas-separation properties. The mechanism of the photochemicalcrosslinking reaction is believed to include the absorption of thephotochemical energy by the benzophenone chromophore, abstraction of thehydrogen atom from the benzylic function of the alkyl substituent on thediamine by an excited high energy state of the benzophenone function,followed by recombination of the resulting free radicals to form thecrosslink. Photochemical mechanisms of this type are described incurrent photochemistry textbooks and are generally accepted by thosepracticing the art. The use of the herein described photochemicalcrosslinking reaction for gas separations membranes is not predicatedupon the actual details of the mechanism and the above suggestedmechanistic details should not limit the use of this invention.

As preferred examples, some of the fully cyclized polyimides of thisinvention are soluble in ordinary organic solvents. This is a greatadvantage for the ease of fabrication of industrially useful membranes.Further, the polyimides reported in this invention range from extremelysoluble to insoluble. The soluble polyimides could be solution cast onporous solvent resistant substrates to serve as the dense separatinglayer of a composite membrane; or they can be solution cast as dense orasymmetric films. Following casting, the membranes can bephotochemically crosslinked to enhance solvent resistance and permeationproperties. Insoluble examples can be cast into membranes from theirpolyamic acid form and subsequently chemically or thermally cyclized.

The photochemically crosslinked polyimides described in this inventiongenerally have greatly reduced solvent sensitivity when compared withthe respective uncrosslinked polyimide. This affords greaterenvironmental stability in the final membrane.

The polyimides described in this invention have high inherent thermalstabilities. They are stable to 400° C. in air or inert atmospheres. Theglass transition temperatures of these polyimides are generally above300° C. The high temperature characteristics of these polyimides canhelp to prevent the membrane compaction problems observed in otherpolymers at even moderate temperatures. These exceptional thermalstabilities are not degraded in the photochemically crosslinked form.

The present invention finds use in recovery of hydrogen in refinery andammonia plants; separation of carbon monoxide from hydrogen in syngassystems; separation of carbon dioxide or hydrogen sulfide fromhydrocarbons; enrichment of oxygen and nitrogen from air for increasedcombustion or inerting streams, respectively.

EXAMPLES EXAMPLE 1

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (600 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(3.22 g, 0.01 mol). After stirring 0.5 hours,5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidenebis-1,3-isobenzofuranedione##STR4## (84.36 g, 0.19 mol, added in eight portions, last portionwashed in with 200 ml N-methyl pyrrolidone) was added at 50° C. Theyellow solution was stirred at 50° C. overnight, then a solution ofacetic anhydride (75.8 mol, 0.80 mol) and triethylamine (112.9 ml, 0.81mol) was rapidly added and the resulting reaction solution stirred for 2hours. The reaction solution was precipitated in methanol. The resultingwhite solid was collected by filtration, washed with methanol and driedin a vacuum oven at room temperature overnight, at 100° C. for 5 hours,and 250° C. for 2 hours to give 104.37 g white product.

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 80° C. with a 15 mil (38×10⁻⁵ m) knife gap. Thefilms were dried on a plate at 80° C. for 25 minutes, cooled to roomtemperature, stripped off the plate and dried in a vacuum oven at roomtemperature overnight and at 120° C. for 4 hours.

Du Pont TEFLON® dry lubricant contains a fluorocarbon telomer whichreduces the adhesion of the membrane to the glass plate.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C.Results are reported below:

He Productivity: 29,300 centiBarrer

N₂ Productivity: 2,270 centiBarrer

CO₂ Productivity: 84,600 centiBarrer

He/N₂ Selectivity: 13

CO₂ /N₂ Selectivity: 37.3

A centiBarrer is the number of cubic centimeters of gas passed by themembrane at standard temperature and pressure times the thickness of themembrane in centimeters times 10⁻¹² divided by the permeating area ofthe membrane in square centimeters times the time in seconds times thepartial pressure difference across the membrane in cm Hg, i.e., ##EQU1##

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 32,230 centiBarrer

H₂ /CH₄ Selectivity: 9.5

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed into N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. Some of thefilm dissolved leaving long strands of crosslinked polymer out ofsolution.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. Results are reported below:

He Productivity: 31,200 centiBarrer

N₂ Productivity: 480 centiBarrer

CO₂ Productivity: 58,400 centiBarrer

He/N₂ Selectivity: 65

CO₂ /N₂ Selectivity: 122

and

He Productivity: 31,000 centiBarrer

N₂ Productivity: 750 centiBarrer

CO₂ Productivity: 62,000 centiBarrer

He/N₂ Selectivity: 41

CO₂ /N₂ Selectivity: 82

The irradiated films prepared above were tested for mixed gas H2/CH4(50/50) permeabilities at 400 psig (276×105 Pa), 25° C. Results areshown below:

H₂ Productivity: 18,560 centiBarrer

H₂ /CH₄ Selectivity: 38.2

EXAMPLE 2

To a stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine (30.01 g,0.20 mol) in N-methyl pyrrolidone (600 ml) under an inert atmosphere wasadded 3,3',4,4'-benzophenone tetracarboxylic dianhydride (6.44 g, 0.02mol, washed in with 50 ml N-methyl pyrrolidone). After the solutionstirred for 0.75 hours,5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidenebis-1,3-isobenzofuronedione(79.92 g, 0.18 mol, added in seven portions, last portion washed in with150 ml N-methyl pyrrolidone) was added and the yellow reaction solutionstirred for 2 hours. A solution of acetic anhydride (75.8 ml, 0.80 mol)and triethylamine (112.9 ml, 0.81 mol) was rapidly added to the reactionsolution and the resulting yellow solution stirred for 2 hours. Thereaction solution was precipitated in methanol. The resulting whitesolid was collected by filtration, washed with methanol and dried in avacuum oven at room temperature overnight, at 100° C. for 3 hours, andat 250° C. for 3 hours to give 119.5 g product.

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 75° C. with a 15-mil (38×10⁵ m) knife gap. Thefilms were dried on the plate at 75° C. for 25 minutes, cooled to roomtemperature, stripped off the plate, and dried in a vacuum oven at roomtemperature overnight and at 120° C. for 4 hours.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C.Results are reported below:

He Productivity: 28,530 centiBarrer

N₂ Productivity: 1,800 centiBarrer

CO₂ Productivity: 129,000 centiBarrer

He/N₂ Selectivity: 16

CO₂ /N₂ Selectivity: 72

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. Some of thefilm went into solution leaving short strands of crosslinked polymer outof solution.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. The results are reported below:

He Productivity: 22,800 centiBarrer

N₂ Productivity: 124 centiBarrer

CO₂ Productivity: 46,000 centiBarrer

He/N₂ Selectivity: 184

CO₂ /N₂ Selectivity: 370

EXAMPLE 3

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(9.21 g, 0.03 mol). After stirring at 50° C. for 0.3 hours,5,5'-2,2,2-trifluoro-2-(trifluoromethyl)ethylidenebis-1,3-isobenzofuranedione(761 g, 0.17 mol, added in four portions, last portion washed in with150 ml N-methyl pyrrolidone) was added and the resulting reactionsolution stirred at 50° C. overnight. A solution of acetic anhydride(78.5 ml, 0.80 mol) and triethylamine (112.9 ml, 0.81 mol) was rapidlyadded and the resulting yellow solution stirred at 50° C. for 2 hours.The reaction solution was precipitated in methanol, the white solidcollected by filtration, washed with methanol and dried in a vacuum ovenat room temperature overnight, at 100° C. for 3 hours and at 220° C. for3 hours to give 104.2 g product.

Films were cast from at 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15 mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature, and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C.Results are reported below:

He Productivity: 28,660 centiBarrer

N₂ Productivity: 1,540 centiBarrer

CO₂ Productivity: 121,650 centiBarrer

He/N₂ Selectivity: 18.6

CO₂ /N₂ Selectivity: 79

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 21,420 centiBarrer

H₂ /CH₄ Selectivity: 13.7

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. The solventbecame slightly colored but the majority of the film remained out ofsolution and unswollen.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. Results are reported below:

He Productivity: 10,300 centiBarrer

N₂ Productivity: 210 centiBarrer

CO₂ Productivity: 24,400 centiBarrer

He/N₂ Selectivity: 49

CO₂ /N₂ Selectivity: 116

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results arereported below:

H₂ Productivity: 22,800 centiBarrer

H₂ /CH₄ Selectivity: 83

EXAMPLE 4

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(16.1 g, 0.05 mol) and the resulting yellow solution stirred for 0.5hours.5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidene-bis-1,3-isobenzofuranedione(66.6 g, 0.15 mol, in four portions, last portion washed in with 150 mlN-methyl pyrrolidone) was added to give a light yellow solution. Afterstirring overnight at 50° C., a solution of acetic anhydride (75.8 ml,0.80 mol) and triethylamine (112.9 ml, 0.81 mol) was rapidly added andthe resulting reaction solution stirred at 50° C. for 2 hours. Thereaction solution was precipitated in methanol, the resulting solidcollected by filtration, washed with methanol and dried in a vacuum ovenat room temperature overnight, at 100° C. for 3 hours and at 200° C. for3 hours. The product was an off-white solid (102.3 g).

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C. Theresults are reported below:

He Productivity: 26,520 centiBarrer

N₂ Productivity: 2,640 centiBarrer

CO₂ Productivity: 90,320 centiBarrer

He/N₂ Selectivity: 10

CO₂ /N₂ Selectivity: 34

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 22,080 centiBarrer

H₂ /CH₄ Selectivity: 14.9

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed into N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. The majorityof the film remained out of solution unswollen with a small amount ofswollen polymer present.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. Results are reported below:

He Productivity: 11,900 centiBarrer

N₂ Productivity: 62.4 centiBarrer

CO₂ Productivity: 25,700 centiBarrer

He/N₂ Selectivity: 191

CO₂ /N₂ Selectivity: 412

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 14,450 centiBarrer

H₂ /CH₄ Selectivity: 53.1

EXAMPLE 5

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(32.2 g, 0.10 mol). After stirring for 2 hours at 50° C.,5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidene-bis-1,3-isobenzofuranediione(44.4 g, 0.10 mol, added in four portions, last portion washed in with150 ml N-methyl pyrrolidone) was added to the slightly yellow reactionsolution. The reaction solution was allowed to stir at 50° C. overnight.A solution of acetic anhydride (75.8 ml, 0.80 mol) and triethylamine(112.9 ml, 0.81 mol) was added as rapidly as possible to the rapidlystirred reaction solution at 50° C. After stirring for 2 hours, thereaction solution was precipitated in methanol. The resulting whitesolid was collected by filtration, washed with methanol, and dried in avacuum oven at room temperature overnight, at 100° C. for 3 hours and at220° C. for 3 hours to give 96.9 g product.

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 10,600 centiBarrer

H₂ /CH₄ Selectivity: 20.0

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed into N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. The solventbecame slightly colored but the film did not dissolve or become swollen.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 6,100 centiBarrer

H₂ /CH₄ Selectivity: 222.4

EXAMPLE 6

To a 50° C. stirred solution of 2,3,5,6-tetramethyl-1,4-phenylenediamine (32.86 g, 0.20 mol) in N-methyl pyrrolidone (500 ml) under aninert atmosphere was sequentially added 3,3',4,4'-benzophenonetetracarboxylic dianhydride (3.22 g, 0.01 mol) and5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidenebis-1,3-isobenzofuranedione(84.36 g, 0.19 mol, added in four portions, last portion washed in with250 ml N-methyl pyrrolidone) and the resulting yellow solution wasstirred overnight at 50° C. A solution of acetic anhydride (75.8 ml,0.80 mol) and triethylamine (112.9 ml, 0.81 mol) was rapidly added tothe reaction solution. After stirring at 50° C. for 2 hours, the yellowreaction solution was precipitated in methanol. The resulting whitesolid was collected by filtration, washed with methanol, and dried in avacuum oven at room temperature overnight, at 100° C. for 4 hours and at250° C. for 3 hours to give 112 g product.

Films were cast from 12.5% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 85° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 85° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C.Results are reported below:

He Productivity: 39,600 centiBarrer

N₂ Productivity: 3,500 centiBarrer

CO₂ Productivity: 230,900 centiBarrer

He/N₂ Selectivity: 11.3

CO₂ /N₂ Selectivity: 66

The above films were tested for mixed gas O₂ /N₂ (21/79) (mole)permeabilities at 300 psig (206×10⁵ Pa), 25° C. Results are reportedbelow:

O₂ Productivity: 14,100 centiBarrer

O₂ /N₂ Selectivity: 3.4

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 33,980 centiBarrer

H₂ /CH₄ Selectivity: 6.8

The above films were irradiated with light from a 50 watt Hanovia lowpressure mercury arc lamp (film 4 inches from lamp) at 25° C. for 1 houron one side. A portion of the film was placed into N-methyl pyrrolidone,a good solvent for the uncrosslinked polymer. A thin unswollen filmsurface remained out of solution along with swollen strands ofphotocrosslinked polymer.

The above irradiated films were tested for mixed gas O₂ /N₂ (21/79)(mole) permeabilities at 300 psig (206×10⁵ Pa), 25° C. Results arereported below:

O₂ Productivity: 4,600 centiBarrer

O₂ /N₂ Selectivity: 6.8

The above irradiated films were consecutively tested for pure gashelium, nitrogen, methane, carbon dioxide, and nitrogen permeabilitiesat 300 psig (206×10⁵ Pa), 25° C. Results are reported below:

He Productivity: 28,159 centiBarrer

N₂ Productivity: 610 centiBarrer

CH₄ Productivity: 106 centiBarrer

CO₂ Productivity: 19,787 centiBarrer

N₂ Productivity: 868 centiBarrer

He/N₂ Selectivity: 46.2

He/CH₄ Selectivity: 266

CO₂ /CH₄ Selectivity: 187

CO₂ /N₂ Selectivity: 22.8

The above non-irradiated films were irradiated with light from a 450watt Hanovia medium pressure mercury arc lamp for 15 minutes on eachside of the film at less than 50° C. A portion of the film was placed inN-methyl pyrrolidone, a good solvent for the uncrosslinked polymer. Someof the film went into solution leaving strands of crosslinked polymerout of solution.

The above irradiated films were tested for mixed gas H2/CH4 (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 31,000 centiBarrer

H₂ /CH₄ Selectivity: 183

The above films were consecutively tested for pure gas carbon dioxide,nitrogen, and helium permeabilities at 400 psig (276×10⁵ Pa), 25° C. Theresults are reported below:

CO₂ Productivity: 16,400 centiBarrer

N₂ Productivity: 410 centiBarrer

He Productivity: 55,500 centiBarrer

He/N₂ Selectivity: 137

CO₂ /N₂ Selectivity: 40

The above irradiated films were tested for mixed gas O₂ /N₂ (21/79)(mole) permeabilities at 300 psig (706×10⁵ Pa), 25° C. The results arereported below:

O₂ Productivity: 2,900 centiBarrer

O₂ /N₂ Selectivity: 7.4

EXAMPLE 7

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (500 ml) under an inertatmosphere was sequentially added 3,3',4,4'-benzophenone tetracarboxylicdianhydride (3.22 g, 0.01 mol) and 1,2,4,5-benzenetetracarboxylicdianhydride (41.44 g, 0.19 mol, added in four portions). After stirringovernight at 50° C., a solution of acetic anhydride (75.8 ml, 0.80 mol)and triethylamine (112.9 ml, 0.81 mol) was rapidly added and theresulting orange solution stirred for 2 hours at 50° C. The reactionsolution was precipitated in methanol. The resulting orange solid wascollected by filtration, washed with methanol, and dried in a vacuumoven at room temperature overnight, at 100° C. for 3 hours and at 250°C. for 3 hours to give 67.1 g product.

Films were cast from at 10% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 80° C. with a 15-mil (38× 10⁻⁵ m) knife gap.The films were dried on the plate at 80° C. for 30 minutes, cooled toroom temperature and dried in a vacuum oven at room temperatureovernight. The films were stripped off the plate and further dried in avacuum oven at 120° C. for 4 hours.

The above films were tested for mixed gas O₂ /N₂ (21/79) (mole)permeabilities at 450 psig (310×10⁵ Pa), 25° C. Results are reportedbelow:

O₂ Productivity: 3,100 centiBarrer

O₂ /N₂ Selectivity: 4.1

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 21,960 centiBarrer

H₂ /CH₄ Selectivity: 9.3

The above films were irradiated with a 50 watt Hanovia low pressuremercury arc lamp (film 4 inches from lamp) for 1 hour at 25° C. on oneside. A portion of the film was placed into N-methyl pyrrolidone, a goodsolvent for the uncrosslinked polymer. The majority of the filmdissolved leaving long strands of swollen crosslinked polymer out ofsolution.

The above irradiated films were tested for mixed gas O₂ /N₂ (21/79)(mole) permeabilities at 300 psig (206×10⁵ Pa), 25° C. Results arereported below:

O₂ Productivity: 2,400 centiBarrer

O₂ /N₂ Selectivity: 6.8

The above non-irradiated films were irradiated with light from a 450watt Hanovia medium pressure mercury arc lamp for 15 minutes on eachside of the film at less than 50° C. A portion of the film was placed inN-methyl pyrrolidone, a good solvent for the uncrosslinked polymer. Themajority of the film dissolved leaving strands of swollen crosslinkedpolymer out of solution.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 18,320 centiBarrer

H₂ /CH₄ Selectivity: 134

EXAMPLE 8

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(6.44 g, 0.02 mol) and the resulting solution stirred for 0.75 hours. At50° C. with stirring, 1,2,4,5-benzenetetracarboxylic dianhydride (39.3g, 0.18 mol, added in four portions, last portion washed in with 150 mlN-methyl pyrrolidone) was added and the orange reaction solution stirredovernight at 50° C. A solution of acetic anhydride (75.8 ml, 0.80 mol)and triethylamine (112.9 ml, 0.81 mol) was added as fast as possible tothe rapidly stirring 50° C. reaction solution. A solid precipitated, butslowly went back into solution. After stirring at 50° C. for 2 hours,the orange reaction solution was precipitated in methanol. The resultingyellow solid was collected by filtration, washed with methanol and driedin a vacuum oven at room temperature overnight, at 100° C. for 3 hoursand at 230° C. for 3 hours. This gave 68.5 g product as yellow-orangesolid.

Films were cast from a 12.5% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15 mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature, and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were consecutively tested for pure gas helium, nitrogen,and carbon dioxide permeabilities at 400 psig (286×10⁵ Pa), 25° C.Results are reported below:

He Productivity: 22,730 centiBarrer

N₂ Productivity: 1,400 centiBarrer

CO₂ Productivity: 118,600 centiBarrer

He/N₂ Selectivity: 16

CO₂ /N₂ Selectivity: 85

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 23,600 centiBarrer

H₂ /CH₄ Selectivity: 9.2

and

H₂ Productivity: 29,380 centiBarrer

H₂ /CH₄ Selectivity: 7.4

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. The filmpartially dissolved leaving long strands of swollen crosslinked polymerout of solution.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. Results are reported below:

He Productivity: 960 centiBarrer

N₂ Productivity: 19.6 centiBarrer

CO₂ Productivity: 2,100 centiBarrer

He/N₂ Selectivity: 49

CO₂ /N₂ Selectivity: 107

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig, 25° C. Results are reported below:

H₂ Productivity: 12,720 centiBarrer

H₂ /CH₄ Selectivity: 81.7

EXAMPLE 9

To a 50° C. stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.01 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(9.21 g, 0.029 mol). After the yellow solution had stirred for 0.50hours, 1,2,4,5-benzenetetracarboxylic dianhydride (37.4 g, 0.17 mol,added in four portions, last portion washed in with 150 ml N-methylpyrrolidone) was added and the resulting orange reaction solutionstirred overnight at 50° C. A solution of acetic anhydride (75.8 ml,0.80 mol) and triethylamine (112.9 ml, 0.81 mol) was added as fast aspossible to the rapidly stirred 50° C. reaction solution. A solidprecipitated, but went back into solution after 3 minutes. The resultingorange reaction solution was stirred at 50° C. for 2 hours and thenprecipitated in methanol. The off-white solid was collected byfiltration, washed with methanol and dried in a vacuum oven at roomtemperature overnight, at 100° C. for 3 hours and at 220° C. for 3 hoursto give 69.4 g of an orange product.

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15 mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature, and dried in a vacuum oven at room temperature overnight.

The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are shown below:

H₂ Productivity: 24,050 centiBarrer

H₂ /CH₄ Selectivity: 8.3

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. A smallamount of the film went into solution, but the majority remained out ofsolution either as swollen strands or unswollen layers of film.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results arereported below:

H₂ Productivity: 12,430 centiBarrer

H₂ /CH₄ Selectivity: 373

EXAMPLE 10

To a stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine (30.05 g,0.20 mol) in N-methyl pyrrolidone (450 ml) at room temperature under anitrogen atmosphere was added 3,3',4,4'-benzophenone tetracarboxylicdianhydride (16.11 g, 0.05 mol, washed in with N-methyl pyrrolidone (50ml)). After stirring at room temperature for 0.5 hours,1,2,4,5-benzenetetracarboxylic dianhydride (32.72 g, 0.15 mol, washed inwith N-methyl pyrrolidone (100 ml)) was added and the yellow solutionallowed to stir for 2 hours. A solution of acetic anhydride (75.84 ml,0.80 mol) and triethylamine (112.94 ml, 0.80 mol) was added as fast aspossible with fast stirring. A white solid precipitated, but went backin to form a viscous golden yellow solution. After stirring 2 hours thereaction solution was precipitated in methanol, the resulting off-whitesolid collected by filtration, and dried in vacuo overnight at roomtemperature, 4 hours at 100° C. and 3 hours at 240° C. to give product(69.3 g).

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 80° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 80° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 10,170 centiBarrer

H₂ /CH₄ Selectivity: 20.4

The above films were tested for mixed gas CO₂ /CH₄ (50/50) (mole)permeabilities at 245 psig (169×10⁵ Pa), 25° C. Results are reportedbelow:

CO₂ Productivity: 9,517 centiBarrer

CO₂ /CH₄ Selectivity: 30

The above films were irradiated with a 50 watt Hanovia low pressuremercury arc lamp for 1.5 hours on one side at 25° C. A portion of thefilm was placed in N-methyl pyrrolidone, a good solvent for theuncrosslinked polymer. The majority of the film went into solutionquickly, but a thin unswollen film remained out of solution.

The above irradiated films were tested for mixed gas CO₂ /CH₄ (50/50)(mole) permeabilities at 245 psig (169×10⁵ Pa), 25° C. Results arereported below:

CO₂ Productivity: 474 centiBarrer

CO₂ /CH₄ Selectivity: 86

The above non-irradiated films were irradiated with light from a 450watt Hanovia medium pressure mercury arc lamp for 15 minutes on eachside of the film at less than 50° C. A portion of the film was placed inN-methyl pyrrolidone, a good solvent for the uncrosslinked polymer. Asmall amount of the film went into solution, but the majority remainedout of solution either as swollen strands or unswollen layers of film.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 5,110 centiBarrer

H₂ /CH₄ Selectivity: 612

EXAMPLE 11

To a stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine (30.05 g,0.20 mol) in N-methyl pyrrolidone (500 ml) was added3,3',4,4'-benzophenone tetracarboxylic dianhydride (32.22 g, 0.10 mol,washed in with 100 ml N-methyl pyrrolidone) at room temperature under aninert atmosphere. The slightly yellow solution was stirred for 0.5 hoursand then 1,2,4,5-benzenetetracarboxylic dianhydride (21.8 g, 0.10 mol,washed in with N-methyl pyrrolidone (100 ml)). The yellow solutionturned more viscous and was stirred for 2 hours at room temperature. Asolution of acetic anhydride (75.84 ml, 0.80 mol) and triethylamine(112.94 ml, 0.80 mol) was rapidly added with fast stirring, causing asmall amount of white solid to precipitate. As the solid redissolved,the solution became a viscous orange-yellow solution. After stirring for2 hours, the reaction solution was precipitated from methanol, the whitesolid collected by filtration, and the reaction product washed withmethanol. The solid was dried in a vacuo overnight at room temperature,3 hours at 100° C. and 3 hours at 220° C. to give 73.6 g product.

Films were cast from a 15% solution of the above polymer (based onweight) in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 75° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 75° C. for 25 minutes, then at roomtemperature for 30 minutes. The films were stripped off the plate anddried at room temperature in a vacuum oven for 4 hours and at 120° C. ina vacuum oven for 4 hours.

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 6,590 centiBarrer

H₂ /CH₄ Selectivity: 31.4

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. Some of thefilm went into solution, but the majority remained out of solutioneither as swollen strands or unswollen layers of film.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results arereported below:

H₂ Productivity: 5,050 centiBarrer

H₂ /CH4 Selectivity: 471

EXAMPLE 12

To a stirred, 50° C. solution of 2,4,6-trimethyl-1,3-phenylene diamine(30.1 g, 0.20 mol) in N-methyl pyrrolidone (350 ml) under an inertatmosphere was added 3,3',4,4'-benzophenone tetracarboxylic dianhydride(48.3 g, 0.15 mol). After stirring for 0.5 hours,1,2,4,5-benzene-tetracarboxylic dianhydride (10.9 g, 0.05 mol, washed inwith 150 ml N-methyl pyrrolidone) was added and the resulting orangesolution allowed to stir at 50° C. overnight. A solution of aceticanhydride (75.8 ml, 0.80 mol) and triethylamine (112.9 ml, 0.81 mol) wasadded as rapidly as possible to the rapidly stirring reaction solutionand the resulting orange solution stirred at 50° C. for 2 hours. Thereaction solution was precipitated in methanol, the off-white solidcollected by filtration, washed with methanol and dried in a vacuum ovenat room temperature overnight, at 100° C. for 3 hours and at 220° C. for3 hours. The off-white product was collected in a 89.8 g yield.

Films were cast from a 12.5% solution (based on weight) of the abovepolymer in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15-mil (38×10⁻⁵ m) knife gap.

The films were dried on the plate at 90° C. for 25 minutes, cooled toroom temperature and dried in a vacuum oven at room temperatureovernight. The films were stripped off the plate and further dried in avacuum oven at 120° C. for 4 hours.

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 6,850 centiBarrer

H₂ /CH₄ Selectivity: 28.3

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed inN-methyl-pyrrolidone, a good solvent for the uncrosslinked polymer. Thefilm remained out of solution but was slightly swollen.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results arereported below:

H₂ Productivity: 3,100 centiBarrer

H₂ /CH₄ Selectivity: 720

EXAMPLE 13

To a stirred solution of 2,4,6-trimethyl-1,3-phenylene diamine (30.5 g,0.2 mol) in N-methyl pyrrolidone (450 ml) was added3,3',4,4'-benzophenone tetracarboxylic dianhydride (9.21 g, 0.029 mol)at 50° C. under an inert atmosphere. After stirring for 30 minutes,5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidenebis-1,3-isobenzofuranedione(19.03 g, 0.043 mol, in three portions) was added. The yellow solutionwas stirred at 50° C. for 15 minutes when 1,2,4,5-benzenetetracarboxylicdianhydride (28.04 g, 0.129 mol, in three portions, last portion washedin with N-methyl pyrrolidone (300 ml)) was added. The resultingorange-yellow reaction solution was stirred at 50° C. under an inertatmosphere overnight. A solution of acetic anhydride (75.8 ml, 0.80 mol)and triethylamine (112.9 ml, 0.80 mol) was added as quickly as possibleto the rapidly stirred reaction solution at 50° C. The resulting orangereaction solution was stirred for 2 hours at 50° C. The reactionsolution was precipitated in methanol, the resulting white solidcollected by filtration, and washed with additional methanol. The whitesolid was dried in a vacuum oven at ambient temperature overnight, at120° C. for 4 hours and at 260° C. for 4 hours to give 77 g product.

Films were cast from a 15% solution (based on weight) of the abovepolymer in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 90° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at 90° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.The films were stripped off the plate and further dried in a vacuum ovenat 120° C. for 4 hours.

The films were consecutively tested for pure gas helium, nitrogen, andcarbon dioxide permeabilities at 400 psig (276×10⁵ Pa), 25° C. Resultsare reported below:

He Productivity: 22,600 centiBarrer

N₂ Productivity: 600 centiBarrer

CO₂ Productivty: 91,000 centiBarrer

He/N₂ Selectivity: 38

CO₂ /N₂ Selectivity: 152

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig, (276×10⁵ Pa), 25° C. Results are reportedbelow:

H₂ Productivity: 25,000 centiBarrer

H₂ /CH₄ Selectivity: 6.1

The above films were irradiated with light from a 450 watt Hanoviamedium pressure mercury arc lamp for 15 minutes on each side of the filmat less than 50° C. A portion of the film was placed inN-methyl-pyrrolidone, a good solvent for the uncrosslinked polymer. Asmall portion of the film dissolved leaving long strands of swollencrosslinked polymer.

The above irradiated films were consecutively tested for pure gashelium, nitrogen, and carbon dioxide permeabilities at 400 psig (276×10⁵Pa), 25° C. Results are reported below:

He Productivity: 12,150 centiBarrer

N₂ Productivity: 40 centiBarrer

CO₂ Productivity: 12,100 centiBarrer

He/N₂ Selectivity: 304

CO₂ /N₂ Selectivity: 303

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results arereported below:

H₂ Productivity: 18,100 centiBarrer

H₂ /CH₄ Selectivity: 281

EXAMPLE 14

N-methyl pyrrolidone (750 ml) was added to a mixture of3,3',4,4'-benzophenone tetracarboxylic dianhydride (64.44 g, 0.20 mol)and 2,4,6-trimethyl-1,3-phenylene diamine (30.5 g, 0.20 mol) at 50° C.in an inert atmosphere with stirring. The resulting golden viscoussolution was stirred at 50° C. for 3 hours. A solution of aceticanhydride (75.84 g ml, 0.80 mol) and triethylamine (112.94 ml, 0.81 mol)was added with stirring at 50° C. causing the color to change fromgolden to a dark orange. After stirring for 1.5 hours at 50° C., theviscous solution was precipitated in methanol and the resulting whitesolid collected by filtration. The polymer was dried in a vacuum oven atroom temperature overnight, at 100° C. for 3 hours and at 200° C. for 4hours to give the product (85.2 g) as a light yellow solid.

Films were cast from a 10% solution (based on weight) of the abovepolymer in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 80° C. with a 15-mil (38×10⁻⁵ m) knife gap. Thefilms were dried on the plate at room temperature, stripped off theplate and dried at room temperature overnight in a vacuum oven, and at220° C. for 6 hours in a vacuum oven.

Differential Scanning Calorimetry (DSC) was performed on the above filmusing a Du Pont Thermal Analyzer Model 990-3 with cell modelHCB1-S/N00523, Baseline scope=5.0 in a nitrogen atmosphere at a 10°C./minute progress rate. No transitions correlatable to a Tg or Tm wereobserved up to 400° C.

Thermogravimetric Analysis (TGA) was performed on the above film using aDu Pont Thermogravimetric Analyzer Model 99-2 with cell Model 951-5 in anitrogen atmosphere at a 10° C./minute progress rate. A 10% weight losswas observed at 565° C. and a 40% weight loss was observed at 695° C.

The above films were tested for mixed gas CO₂ /CH₄ (50/50) (mole)permeabilities at 250 psig, (172×10⁵ Pa), 25° C. Results are reportedbelow:

CO₂ Productivity: 3,746 centiBarrer

CH₄ Productivity: 115 centiBarrer

CO₂ /CH₄ Selectivity: 32.4

or

CO₂ Productivity: 3,796 centiBarrer

CH₄ Productivity: 122 centiBarrer

CO₂ /CH₄ Selectivity: 31

The above films were irradiated with light from a 50 watt Hanovia lowpressure mercury arc lamp (film 4 in. from lamp)for 1.5 hours on oneside of the film at 25° C. A portion of the film was placed inN-methyl-pyrrolidone, a good solvent for the uncrosslinked polymer. Thefilm did not dissolve or swell after prolonged contact.

Differential Scanning Calorimetry (DSC) was performed on the aboveirradiated film using a Du Pont Thermal Analyzer Model 990-3 with cellmodel HCB1-S/N00523, Baseline scope=5.0 in a nitrogen atmosphere at a10° C./minute progress rate. No transitions correlatable to a Tg or Tmwere observed up to 400 ° C.

Thermogravimetric Analysis (TGA) was performed on the above irradiatedfilm using a Du Pont Thermogravimetric Analyzer Model 99-2 with cellModel 951-5 in a nitrogen atmosphere at a 10° C./minute progress rate. A10% weight loss was observed at 565° C. and a 40% weight loss wasobserved at 695° C.

The above irradiated films were tested for mixed gas CO₂ /CH₄ (50/50)(mole) permeabilities at 250 psig (172×10⁵ Pa), 25° C. The results arereported below:

CO₂ Productivity: 95.4 centiBarrer

H₂ /CH₄ Selectivity: 93.3

EXAMPLE 15

To a stirred solution of 2,3,5,6-tetramethyl-1,4-phenylene diamine(24.64 g, 0.15 mol) in N-methyl pyrrolidone (400 ml) under an inertatmosphere at room temperature was portionwise added3,3',4,4'-benzophenone tetracarboxylic dianhydride (48.33 g, 0.15 mol,added in four portions, last portion washed with N-methyl pyrrolidone(120 ml)). After stirring 3 hours at room temperature, a solution ofacetic anhydride (56.88 ml, 0.60 mol), and triethylamine (84.21 ml, 0.60mol) was rapidly added causing a white solid to precipitate out of thelemony yellow solution. The solid went back into solution to form darkorange viscous solution which was stirred at room temperature for 2hours. The reaction resulting solid collected by filtration, washed withmethanol and dried in a vacuum oven at room temperature overnight, at100° C. for 3 hours and at 220° C. for 3 hours to give a 66.6 g product.

Films were cast from a 15% solution (based on weight) of the abovepolymer in N-methyl pyrrolidone onto a glass plate treated with Du PontTEFLON® dry lubricant at 80° C. with a 15-mil (38×10⁻⁵) knife gap. Thefilms were dried on the plate at 80° C. for 25 minutes, cooled to roomtemperature and dried in a vacuum oven at room temperature overnight.

The films were stripped off the plate and further dried in a vacuum ovenat 100° C. for 4 hours.

The above films were tested for mixed gas CO₂ /CH₄ (50/50) (mole)permeabilities at 245 psig (171×10⁵ Pa), 25° C. Results are reportedbelow:

CO₂ Productivity: 2,671 centiBarrer

CO₂ /CH₄ Selectivity: 8.5

The above films were tested for mixed gas H₂ /CH₄ (50/50) (mole)permeabilities at 400 psig (276×10⁵ Pa), 25° C. The results are reportedbelow:

H₂ Productivity: 3,350 centiBarrer

H₂ /CH₄ Selectivity: 25.2

The above films were irradiated with light from a 50 watt Hanovia lowpressure mercury arc lamp (film 4 in. from lamp) for 1 hour on one sideat 25° C.

The film turned color from clear yellow to clear orange. A portion ofthe film was placed in N-methyl pyrrolidone, a good solvent for theuncrosslinked polymer. The majority of the film became swollen but didnot go into solution.

The above irradiated films were tested for mixed gas CO₂ /CH₄ (50/50)(mole) permeabilities at 245 psig (171×10⁵ Pa), 25° C. Results arereported below:

CO₂ Productivity: 243 centiBarrer

CO₂ /CH₄ Selectivity: 124

The above non-irradiated films were irradiated with light from a 450watt Hanovia medium pressure mercury arc lamp for 15 minutes on eachside at less than 50° C. A portion of the film was placed in N-methylpyrrolidone, a good solvent for the uncrosslinked polymer. The filmremained out of solution but was slightly swollen.

The above irradiated films were tested for mixed gas H₂ /CH₄ (50/50)(mole) permeabilities at 400 psig (276×10⁵ Pa), 25° C. Results arereported below:

H₂ Productivity: 2,760 centiBarrer

H₂ /CH₄ Selectivity: 312

I claim:
 1. A process for separating gases comprising bringing a mixtureof two or more gases under pressure into contact with a membrane formedof a photochemically crosslinked aromatic polyimide of the formula##STR5## or mixtures thereof --X,--X₁, --X₂, and --X₃ are independentlyprimary or secondary alkyl group having 1 to 6 carbon atoms preferablymethyl or ethyl,--Z is --H, --X, --X₁, --X₂, or --X₃ and --R" is##STR6## (where n=0 to 4) or alkylene radicals of 1 to 3 carbon atomsand from 5 to 100% of --R-- and R' are R, whereby at least one of saidgases is enriched upon permeating the membrane.
 2. The process of claim1 wherein --X, --X₁, --X₂, and --X₃ are --CH₃ or --C₂ H₅.
 3. The processof claim 2 wherein ##STR7##
 4. A gas separation membrane formed of aphotochemically crosslinked aromatic polyimide of the formula ##STR8##or mixtures thereof --X, --X₁, --X₂, and --X₃ are independently primaryor secondary alkyl groups having 1 to 6 carbon atoms preferably methylor ethyl,--Z is --H, --X, --X₁, --X₂, or --X₃ and --R" is ##STR9##(where n=0 to 4) or alkylene radicals of 1 to 3 carbon atoms and from 5to 100% of --R-- and R' are R.
 5. The membrane of claim 4 wherein --X,--X₁, --X₂, or --X₃ are --CH₃ or --C₂ H₅.
 6. The membrane of claim 5wherein ##STR10##